1. Field of the Invention
This invention relates to a fuel injector nozzle provided with a needle lift sensor, particularly for internal combustion engines, comprising a nozzle holder, which contains a valve needle, which is biased by a spring toward a closing position against the pressure of the liquid that is to be injected, wherein the needle lift sensor is contained in the nozzle holder and responsive to the position of the valve needle and includes a movable shielding member, which is mounted on that end of the valve needle which is remote from the valve seat or on a spring seat secured to said end of the valve needle.
2. Description of the Prior Art
Internal combustion engines operating with fuel injection, particularly in diesel engines, are provided with fuel injection nozzles having a needle valve, which opens against the force of a valve spring when the pressure of the fuel delivered by the fuel injection pump rises to a predetermined value and which closes in response to a pressure drop. It is desirable to ascertain the exact time when the fuel injection begins and the duration of the fuel injection pulse because the fuel consumption rate can be determined from said parameters. The fuel consumption rate can be used for an indication of various data, such as the fuel consumption and the remaining cruising range, and for automatic control functions, e.g., in order to minimize the fuel consumption and the polluant content in the exhaust gas and to optimize the load on the engine.
A fuel injector nozzle of the kind described first hereinbefore has been disclosed in Published German Application No. 29 20 669. In that known valve a movable shielding member consisting of soft magnetic material is secured to a spring seat, which is secured to the top end of the valve needle. The shielding member is movable in the gap between a permanent magnet and a Hall effect sensor in such a manner that the Hall effect sensor will be exposed to or shielded from the magnetic field of the permanent magnet in dependence on the position of the valve needle.
A similar fuel injector nozzle disclosed in U.S. Pat. No. 4,366,706 comprises a small permanent magnet, which is secured to the spring seat and faces a Hall effect sensor, which is carried by a cylindrical bracket that is surrounded by the valve spring.
Published German Application No. 30 04 424 discloses a fuel injector nozzle in which the valve needle is provided at its top end with a pin, which constitutes a core extending in a stationary cylindrical coil. A movement of the valve needle and of the pin will change the inductance of the coil as an indication of the position of the valve needle.
In the fuel injector nozzles disclosed in Published German Application No. 29 20 669 and U.S. Pat. No. 4,366,706 the output voltage of the Hall effect sensor depends on the relative position of the magnet and of the valve needle. The beginning and duration of the fuel injection pulse can be determined from that output signal. But that known concept involves various disadvantages. In the first place, Hall effect sensors are expensive and delicate components and particularly the temperature rise and the vibration involved in the operation of an internal combustion engine will adversely affect the reliability of operation and the life of the sensor and the accuracy of the measurement. Errors may also be introduced into the measurement by stray electric or magnetic fields, which are inevitable in a motor vehicle. Owing to the design of the sensor the output signal is an analog signal so that a separate circuit is required for its utilization and the relative position of the magnet and the Hall effect sensor must be determined by a precise adjustment.
In accordance with Published German Application No. 32 41 390 an optical glass fiber line is used in conjunction with a fuel injector nozzle and serves to transmit light generated by a combustion flame.